This invention relates to portable motorised equipment for digging a trench into the ground, particularly hand-held equipment, and includes attachments for existing hand-held power units.
The power digging of holes or trenches is many times faster than manual digging with hand tools. Because of the considerable horsepower needed to drive a chain or mechanical digger, its weight and size, and the need for stable control of the digging bar or bucket, virtually all mechanical digging tools are mounted on a custom made vehicle. This makes them physically large, expensive, impractical, or uneconomic to own or to use for small jobs, and difficult to transport, typically requiring a second vehicle to take them from place to place.
On many occasions about a house, a farm, or at construction sites, there is a need to bury a relatively small conduit down to perhaps 1 meter deep within the groundxe2x80x94typical conduit diameters being about 25 mm for examples such as telephone cables, for water pipes about a farm, or small mains power cables. It is wasteful to dig a trench for such a thin conduit with hand tools which are usually about 150 mm wide or more, or to use one of the previously mentioned chain or mechanical diggers.
Observing the power and degree of control available from a chain saw style power unit, experiments have taken place to ascertain whether a useful and cost-effective trench digger could be created using a chain-saw as a power unit. Chain-saws are widely distributed, there being about 25,000 chain-saws sold in New Zealand (about one per 120 persons) per annum. It appears preferable to direct the invention towards providing an attachment capable of being reversibly attached to an existing chain-saw, for those who already possess a chain-saw. The blade is usually held in place with two bolts.
A review of the prior art in this general area reveals: (1) U.S. Pat. No. 4,429,477 Tice et al, who describe a modified chain-saw, including a gear reducer, for digging (and particularly deals with digger chain tooth design) (2) U.S. Pat. No. 4,651,449 Rose. (3) U.S. Pat. No. 4,922,763 Ashworth where an ordinary chain-saw is provided with a catcher for dragged-up soil, to serve as a soil sampler, and (4) the more extreme U.S. Pat. No. 4,799,320 West et al (which provides horizontally aimed augers to each side of the far end of a chain-saw blade). (5) U.S. Pat. No. 4,660,306 Bruce et al describes a trencher attachment for use on the arm of a hydraulic excavator. There is a group of patents for digging chains for dedicated excavators. Example chain patents are: U.S. Pat. No. 6,154,987 Rumer et al, U.S. Pat. No. 4,924,609 Martin, U.S. Pat. No. 4,893,464 Thuerman, U.S. Pat. No. 4,651,449 Rose (this chain is for a chain-saw), U.S. Pat. No. 3,913,979 Strauss et al, and U.S. Pat. No. 3,846,922 Horton.
The problem to be solved might be stated as xe2x80x9cto provide a cheap, portable powered trenching machine able to be held by a person while in usexe2x80x9d.
It is an object of this invention to provide means for the portable, motorised digging of a trench or at least to provide the public with a useful choice.
In a first broad aspect this invention provides a hand-held, self-contained motor-driven trenching device for cutting a slit within a substrate, wherein the trenching device includes a driven digging chain in the form of an endless loop, having attached teeth, the chain surrounding an outwardly and downwardly protruding cutting beam and being capable of being pulled along a side of the cutting beam by means of a driven rotatable chain engagement means, and wherein the cutting beam is placed substantially in line with the centre of mass of the trenching device, so that the weight of the trenching device falls evenly on the cutting beam when in use to cut a slit in the substrate, and so that in use a person holding the motor-driven trenching device does not experience undue sideways pressure.
Preferably the spacing along the shaft between the driven sprocket and the primary chain receiving sprocket is sufficient to place the driven sprocket in line with the centre of gravity of the assembled chain-saw and attachment, so that in use a person holding the assembly does not experience a sideways torque caused by an unbalanced mass.
Optionally that spacing along the shaft may be adjustable, so that different chain-saw drive units can be employed.
Preferably the driven sprocket is attached to the shaft using a key or spline.
In a second broad aspect this invention provides a for use in cutting a groove or trench in a substrate, wherein the trenching device is comprised of a chain-saw motor drive unit and a trenching attachment adapted for use with the chain-saw motor drive unit; said trenching attachment being capable of repeated attachment to and removal from the chain-saw motor drive unit as a substitute for the original cutting chain and saw blade of the chain-saw.
In a related aspect the trenching attachment includes coupling means capable of being firmly yet reversibly attached to the chain-saw drive unit by means of at least one fastener; said coupling means being attached to a digging chain support means, comprising a first driven sprocket and a nose (idler) sprocket held apart by an elongated cutting beam lying in line with and between the sprockets, wherein the distance between the first driven sprocket and the nose sprocket is adjustable (so that a digging chain in the form of an elongated loop can be tightened and held tightly between the sprockets and around the elongated beam), digging chain support means also comprising at least one sliding surface along at least one side of said elongated beam, drive connection means to couple the first driven sprocket with a second driven sprocket capable of accepting the output of the chain-saw motor by means of an endless primary drive chain capable of being attached to the powered sprocket of the chain-saw drive unit, said means comprising a rotatable shaft supported in perpendicular relationship to the elongated beam, the shaft having the first driven sprocket affixed in line with the elongated beam, the shaft also serving to laterally displace the primary drive chain to one side of the digging chain, so that the cutting beam may be placed substantially in line with the centre of mass of the trenching device regardless of the position of the powered sprocket of the chain-saw drive unit.
Preferably the trenching attachment further includes shaft speed reduction means, so that when in use the digging chain is pulled along the elongated beam at a velocity which is slower than that of the primary drive chain while the motor of the chain-saw drive unit is able to rotate at a preferred rate.
In a related aspect the second driven sprocket capable of accepting the output of the chain-saw motor has a larger circumference than that of the powered sprocket of the chain-saw drive unit.
Preferably a shaft speed reduction means is included within the accessory, so that when in use the digging chain is pulled along the elongated beam at a velocity which is slower than that of the primary endless chain, yet with more force, and a preferred reduction of velocity is to about 40% of initial velocity, although this factor depends on digging chain configuration and soil characteristics.
In a further related aspect the second driven sprocket has about three tines as many teeth as does the powered sprocket of the chain-saw drive unit.
In a third broad aspect the trenching attachment is further provided with ground rest means, said ground rest means comprising one or more bars attached at one end to the trenching attachment, each bar including intermediate ground contact areas, and each bar terminating in a handle.
Preferably each intermediate ground contact area comprises a wheel.
In a fourth broad aspect the attachment further includes a first guard capable of enclosing the primary chain, when in use, and a second guard capable of partially enclosing the first driven sprocket, so that when using the device a person is reasonably protected from injury and from flying debris.
In a fifth broad aspect the invention provides an attachment further including means for sensing electric current flow, so that a person is warned of electrical hazards derived from underground cables when using the device.
In a sixth broad aspect the invention provides a digging chain, the digging chain being in the form of an endless loop of roller chain, provided with projecting teeth on one side; the teeth including a left-hand, a right-hand and a central cutting type of tooth.
The descriptions of the invention to be provided herein are given purely by way of example and are not to be taken in any way as limiting the scope or extent of the invention.